1. (Field of the Invention)
This invention relates to a control apparatus for an electromagnetic force-driven valve, which apparatus opens and closes the suction/exhaust valve of an engine by an electromagnetic force produced by an electromagnet.
2. (Description of the Prior Art)
In an ordinary engine, a valve is controlled to open and close so that a cylinder may perform a suction/exhaust operation.
In one example of a drive apparatus for opening and closing such a suction/exhaust valve, a cam shaft, which is obtained by disposing cams for suction and exhaust on one shaft, is provided on the upper portion of the engine or on one side face thereof. A crankshaft, which is the rotary shaft of the engine, and the cam shaft are connected by rotary transmission means such as a belt, and the cam shaft is driven rotatively in synchronism with the rotational phase of the engine. The axial end face of the valve is pushed by the cam face of the cam shaft via a link mechanism such as a rocker arm or pushing rod. The suction/exhaust valve normally is held in the closed state by a spring and its axial end face is opened by being pushed.
In another example of a drive apparatus for opening and closing a suction/exhaust valve, a suction cam shaft having a suction cam and an exhaust cam shaft having an exhaust cam are disposed on the upper portion of an engine, the cam face of the suction cam shaft pushes the axial end face of the suction valve directly, and the cam face of the exhaust cam shaft pushes the axial end face of the exhaust valve directly, thereby opening the suction/exhaust valve.
This conventional drive apparatus for opening and closing the suction/exhaust valve results in a large-size engine because the cam shaft and link mechanism must be added onto the engine. Furthermore, since the cam shaft and link mechanism are driven by the output shaft of the engine, some of the engine output is consumed by frictional resistance when the cam shaft and link mechanism are driven. This diminishes the effective output of the engine.
Further, the actuation timing of the suction/discharge valve cannot be altered during engine operation. Since the valve actuation timing is adjusted so as to attain high efficiency in a case where the engine is running at a prescribed rpm, engine efficiency declines when it is running at an rpm different from the prescribed rpm.
In order to solve the foregoing problems, an apparatus for driving a suction/exhaust valve to open and close the same by electromagnetic force from an electromagnet, without relying upon a cam shaft, has been disclosed in Japanese Patent Application Laid-Open (KOKAI) Nos. 58-183805 and 61-76713.
The applicant has filed an application relating to an electromagnetic force-driven valve control apparatus adapted to increase engine output when the engine is rotating and low speed, and to improve fuel economy (Japanese Patent Application No. 63-264831). When the valve is controlled by such an electromagnetic force, the valve strikes the cylinder head and bounces back after being seated if the engine is rotating at high speed. Such valve bounce results in diminished fuel economy and unstable engine rotation and is an impedement to high-speed rotation of the engine. For these reasons, accurately sensing engine speed, the amount of valve jump relative to the cylinder and valve open/close timing is essential in order to drive the engine efficiently and stably.
However, the conventional control apparatus for the electromagnetic-force driven valve is adapted to apply, immediately before valve seating, corrective acceleration in the valve-lift direction, namely in the opposite direction, with respect to the driving force acting in the valve-seating direction and stipulating the period during which the valve is in the open state, thereby reducing valve velocity to suppress the amount of jump relative to the cylinder. Consequently, the bounce force differs depending upon the state of the engine load and the engine rotational speed, as a result of which proper deceleration control cannot be achieved.
The present invention has been devised in order to solve the foregoing problems and its object is to provide an electromagnetic force-driven valve control apparatus whereby the open/closed state of an electromagnetically driven valve is sensed reliably to make it possible to accurately control the bounce force acting upon the lifting side even at the time of high-speed rotation.